A typical filling device has a product space that opens into a filling valve. A typical filling valve has an actuator that moves first and second valve elements relative to each other. These valve elements bear against each other in the region of a sealing face when the valve is closed. Otherwise, they are spaced apart.
In some embodiments, a cylindrical valve housing forms the first valve element, while a thickened valve stem forms the second valve element. This second valve element typically has an O-ring seal in the region of its sealing face.
Even when designed as prescribed, such an O-ring seal exhibits play between the edges of the O-ring groove and the O-ring itself. In particular, as the valve opens and closes, contact pressure against the valve's housing tends to deform the O-ring seal slightly. As a result, product can accumulate between the O-ring groove and the O-ring seal. This can be a problem, particularly when the filling product includes solid constituents.